Capacity-compensated motor-driven antenna



Aug. 25, 1964 .1. L. DOONER 3,146,450

CAPACITY-COMPENSATED MOTOR-DRIVEN ANTENNA Filed Feb. 1, 1961 2 Sheets-Sheet 1 mg 77 r a; I 7/ I5" INVENTOR.

/ 0 JohnL.Do.oner

I xvvmvrrs United States Patent 3,145,450 CAPACITY-COMPENSATED MOTOR-DRIVEN ANTENNA John L. Donner, Cedar Grove, NJ assignor to General Bronze Corporation, Garden City, N.Y.

Filed Feb. 1, 1961, der. No. 86,513 Cliairns. :21. 343-723) This invention relates to a whip-type antenna comprising a plurality of sections which are telescopically extensible and retractable. Antenna devices of this type are particularly adapted for use with portable-type radio receivers and transmitters, e.g., radio receivers installed in automobiles, etc.

While antennas of the instant type are broadband devices and operate efficiently over the entire broadcast band, they have an objectionable feature of protruding above the body of an automobile. Being thus exposed, the antennas are generally too long to be left at all times in a fully extended position as they are subject to damage. Accordingly, these antennas are retracted from time to time to different lengths by automobile owners.

However, it is known that the distributed capacitance across an antenna of the instant type is proportional to and varies with changes in the length of the device. In some types of antennas, this distributed capacitance may vary as much as eight micromicrofarads over its entire range of structure, i.e., from a fully retracted position and a fully extended position. As these variations in distributed capacity appear across the input of the radio receiver, e.g., the first tuned circuits, their eflect is to vary the gain and sensitivity of the radio receiver across the broadcast band. However, if this distributed capacity were to remain constant on a tuning of the antenna device, the gain and sensitivity of the radio receiver would remain constant along the entire broadcast spectrum and maximum quality operation thereof achieved.

It is, accordingly, one object of this invention to pro vide an improved extensible-retractable antenna wherein the distributed capacity is substantially constant over its entire range of length adjustment.

Another object of this invention is to provide an improved antenna of the instant type wherein variations in distributed capacity to ground are automatically compensated over its entire range of length adjustment.

Another object of this invention is to provide an improved antenna of the instant type which is tunable over the entire broadcast band while not affecting the gain and sensitivity of a radio receiver connected to the antenna.

These and other objects and advantages of this invention are achieved by the provision of a variable capacitive arrangement which is controlled in accordance with extensions and retractions of the antenna to compensate for resulting variations in distributed capacity between the antenna and ground.

In accordance with an illustrative embodiment of this invention, the telescopic sections of the antenna are extended and retracted by means of a flexible cable which is secured at one end to the innermost one of the sections and operatively engaged by a metallic cable-driving gear. A cable reel mechanism is rotatably mounted adjacent the cable-driving gear on a fixed central shaft to receive or dispense the flexible cable as it is driven in or out by the cable-driving gear. Threadedly mounted on the same shaft and disposed within and keyed to the cable reel mechanism for rotation therewith and for axial movement relative thereto is one plate of the compensating capacitor arrangement; the metallic cabledriving gear, being electrically integral with the antenna device through the medium of flexible cable, functions as ice the other plate of the compensating capacitor arrangement. As the length of the antenna is changed to vary its distributed capacitance to ground, the rotation of the cable reel mechanism and of the movable capacitor plate moves the plate along the threaded central shaft and varies the spacing of the two plates of the compensating capacitor arrangement and therefore the value of compensating capacity introduced into the antenna system.

A fuller understanding of this invention may be had upon a consideration of the description hereinafter set forth, in conjunction with the accompanying drawings wherein:

FIGURE 1 is a side elevational view of the housing assembly of the antenna device embodying the principles of this invention showing the relative positions of a motor housing, cable housing and an antenna housing.

FIGURE 2 is a vertical sectional view taken along the line 22 of FIGURE 1.

FIGURES 3, 4 and 5 are vertical sectional views taken respectively along the lines 3-3, 4-4 and 55 of FIG- URE 2. V H

FIGURE 6 is a graph illustrating the variation of compensating capacity in accordance with the antenna position.

Referring to FIGURE 1, the antenna device of the present invention may be advantageouslycontained in a housing assembly which comprises an antenna housing 1 for storing the telescopic sections of the antenna, a cable housing 3 containing the cable driving gear mechanism and the cable reel mechanism, and a motor housing 5 containing a reversible electric motor, not shown, of well known type for operating the cable-driving mechanisms.

The housing of FIGURE 1 is generally mounted in a substantially upright position, as shown, beneath'the fender 7 of an automobile by a pair of toggle members 11 pivotally mounted on the antenna housing 1; The threaded, upper portion 13. of the antenna housing 1 extends through an opening 15 in the fender 7 and is engaged by a nut 17. The nut 17 bears downwardly against a generally hemispherical insulator 19 which, in turn, bears down against a rubber washer .21 interposed between it and the outer surface of the fender 7. The sharpened upper edges of the toggle members 11 cut into the underside of the fender 7 and effectively ground the housing thereto. Projecting from the lower end of the housing is a mounting screw 9 which "is connected to the frame of the automobile by a metal strap (not shown) to prevent mechanical vibration and also augment the ground connection of the housing.

The antenna, illustrated in FIGURE 4 as fully retracted within the antenna housing 1, includes 'four sections: an innermost section 23 comprising a flexible steel rod; two intermediate tubular sections 25 and 27;and a fixed outer tubular section 29. Each of the sections 23 through 29 is longitudinally slidable relative to its adjacent outer section so that the antenna device is telescopically extensible from or retractable into the antenna housing 1 in conventional fashion. 7

The outer section 29 of the antenna is fixedly supported in insulated relationship within the antenna housing 1 by a plastic spacer 31 which is positioned by the retaining screws 33. The telescopic movements of the inner sections 25 and 27 within the outer section 29 are guided by the bushings 35 and 37, respectively, fixed to their lower ends and also the similar headings 41 near the upper ends of the next adjacent sections 27 and 29, respectively. In addition, the bushings 35 and 37 limit retraction of the inner sections 25 and 27 on engagement with internal circumferential headings 39 which are formed in the next adjacent sections 27 and 29, respectively. The collars 35 and 37 also serve to limit extension of the inner sections (I 25 and 27 on engagement with the similar headings 41 on the sections 27 and 29, respectively.

Retraction of the innermost section 23 is limited by engagement of a finial or tip 43 fixed at its upper end with the end of the adjacent inner section 25. Extension of the innermost section 23 is limited by engagement of the beading 45 near the upper end of the adjacent section 25 with the ferrule 47 by which the lower end of the innermost section is connected to the upper end of a flexible cable 49. As hereinafter further described, the flexible cable 49 extends into the cable housing 3 and is driven so as to extend or retract the antenna device and, also, to control the compensating capacitor arrangement of this invention whereby resulting variations in the distributed capacity across the antenna device are compensated.

The flexible cable 49 comprises a resilient steel wire forming a core which has coiled around and fixed to its surface a helical steel spring 50 with spaced turns acting as a flexible rack. The flexible cable or rack 49 is forced up or pulled down through a central passageway in the insulated spacer 31 and along a guide tube 51 which communicates with the cable housing 3. In being forced upward along the guide tube 51, the flexible rack 49 forces the innermost section 23 to extend and pick up successive ones of the sections 25 and 27 until such time that the antenna device is fully extended. Conversely, the flexible rack 49, on being pulled downward along the guide tube 51, carries along the innermost section 23 of the antenna device which picks up successive sections until the antenna device is fully retracted in the antenna housing 1 as shown in FIGURE 4.

The flexible rack 49 extends into the cable housing 3 which, as illustrated in FIGURE 2, is preferably a metal casting 53 having a central chamber, not designated, for receiving the cable-driving mechanism, hereinafter described in detail. The open end of the casting 53 is normally sealed by a cap 54. Integrally formed on the casting 53 are a pair of chamber extensions 55 and 57 for seating the antenna housing 1 and the motor housing 3, respectively. Centrally disposed in the base of the chamber is a cavity 59 into which is press-fitted the knurled end of a shaft 61. An insulating sleeve 63 is slipped over and positioned on the left end portion of the shaft 61 for rotatably mounting a motor-driven clutch plate assembly 65,

shown also in FIGURE 3, and a cable-driving gear 67, shown also in FIGURE 4, which comprise the cable-driving mechanism.

The insulating sleeve 63 has a shoulder portion at one end against which the clutch plate assembly 65 abuts whereby the face of the clutch plate assembly is removed from the wall of the chamber. The cable-driving gear 67, on the other hand, is retained on the insulating sleeve 63 by a retaining ring 73. The web portion 69 of the clutch plate assembly 65 is formed of insulating material such as nylon or plastic and the rim portion 71 is formed of a hard material such as steel. The cable-driving gear 67, on the other hand, is formed entirely of metal and,

as hereinafter described, functions as one plate of the compensating capacitor arrangement of this invention. It

should be noted that the cable-driving gear 67 is electrically insulated from the shaft 61 and the housing 53 by the sleeve 63.

Referring to FIGURE 2, the cable-driving gear 67 is engaged by the clutch plate assembly 65 by means of ball bearings 75 which are resiliently urged by springs 7'7 into the spaces between a series of spaced buttons 79 projecting a short distance from the left face of the cabledriving gear. The ball bearings 75 and the springs 77 associated therewith are positioned within cavities in the clutch plate assembly 65. The engagement of the ball bearings 75 in the spaces between pairs of adjacent buttons 79 causes rotation of the cable-driving gear 67 when the clutch plate assembly 65 is driven. However, when the resistance to movement of the cable-driving gear 65 is sufficiently great, which occurs when the antenna device is either fully extended or fully retracted, the ball bearings 75 are cammed away from the cable-driving gear 67 by the buttons 79, allowing incremental slippage or indexing of the clutch plate assembly 65 until the motor is turned off.

As shown in FIGURE 3, the rim portion 71 of the clutch plate assembly 65 is serrated to mesh with a worm gear 81 mounted on the shaft 83 of a reversible motor, not shown, of conventional type which is disposed within the motor housing 5. The shaft 83 of the motor continues beyond the Worm gear 81 and is seated on a ball bearing 85 contained within a cavity at the base of the chamber 57 which resists the thrust imposed upon the shaft 83 on the worm gear 81. Thus the clutch plate assembly 65 and the cable-driving gear 67 are rotated in either direction to extend or retract the antenna as desired.

As particularly shown in FIGURE 4, the cable-driving gear 67 is positioned so that the axis of the guide tube 51 is substantially tangential therewith. The cable-driving gear 67 is provided with serrated edges which engage the successive convolutions of the steel spring 50 of the flexible rack 49. Rotation of the cable-driving gear 67 forces the flexible rack 49 upward or downward along the guide tube 51 through the central opening in the insulating spacer 31 and into the antenna housing 1 to vary the length of the antenna. The engagement of the flexible rack 49 and the cable-driving gear 67 is insured by an angular guide ring 87. The flexible rack 49 is directed through the guide ring 87 along a passageway 89 which is axially aligned with the guide tube 51. As shown, this passageway 89 continues as a channel 91 along the inner surface of the guide ring 87 whereby the flexible rack 49 is operatively engaged along a substantial portion of the periphery of the cable-driving gear 67. In the area designated 93 in FIGURE 4, the channel 91 is deflected from the plane of the cable-driving gear 67 and becomes of gradually increasing diameter. As the flexible rack 49 is resilient, it continues to lie against the base of the channel 91 so as to be disengaged from the cable-driving gear 67 slightly beyond the area 93. The flexible rack 49 is thereupon directed along the deflected portion of the guide ring 87 to be stored in a cable reel 95 as shown in FIGURES 2 and 5.

The cable reel 95 is rotatably mounted on shaft 61 adjacent the cable-driving gear 67 on a bushing having an elongated sleeve 99. The bushing 97 is fixed on the shaft 61 by a screw 101 and associated washer elements 103. The cable reel 95 is of cup-like shape with an annular opening 105 in its flanged portion to provide a stor age chamber for the flexible rack 49. The annular opening 105 is aligned with the deflected portion of the channel 91 as it appears at the right-hand edge of the guide ring 87, as shown at 107 in FIGURES 2 and 4. Accordingly, the guide tube 51, the channel 91 and the annular opening 105 form, in effect, a smooth, continuous passageway for movement of the flexible rack 49 between the antenna housing 1 and the cable housing 3. As the cable reel 95 is rotatably mounted on the shaft 61, the flexible rack 49 may be pushed into or pulled from the annular opening 105 by the cable-driving gear 67 without appreciable friction.

Within the cavity of the cup-shaped cable reel 95 is a dished metal plate 109 which, together with the metallic cable-driving gear 67, forms a variable capacitor to compensate for variations in the distributed capacity across the antenna device resulting from an extension or retraction thereof. The plate 109 has a central axial opening which is threadedly engaged on the outer surface of the bushing sleeve 99. The plate 109 is provided at its periphery with radial slots 111 which engage spiders 113 extending radially inward from the inner wall of the cable reel 95. Accordingly, rotation of the cable reel 95 on retraction or extension of the antenna device causes the plate 109 to be driven longitudinally of the shaft 61. It is to be noted that the plate 109 is grounded through bushing sleeve 99, shaft 61 and cable housing 3, which is grounded by the toggle members 11 and the mounting screw 9.

This translational movement of the plate 1tl9 varies its spacing from the cable-driving gear 67, and the value of electrical capacity between them. As the metallic cable-driving gear 67 is electrically integral with the antenna through the flexible rack 49, the capacity of the plate 1599 and cable-driving gear 67 is efiectively in parallel with the distributed capacitance between the antenna device and ground.

Electrical connection is made from a radio receiver or other radio equipment, not shown, to the antenna through a coaxial fitting 115 formed on the skirt of the antenna housing 1. An annular plastic spacer 117 within the antenna housing 1 supports an annular wiper 119 in electrical contact with the outer section 29 of the antenna. Projecting from the annular wiper 119 is a prong 125? which extends through the annular spacer 117 and through the skirt of the housing 1 into the fitting 115 to form a conventional coaxial male connector to which may be connected a female connector at one end of a coaxial cable extending to the input of the radio receiver or other radio equipment.

As hereinabove mentioned, the distributed capacitance of a typical antenna device is increased, for example, approximately eight micromicrofarads as the antenna is moved to from a fully retracted to a fully extended posi tion. As this occurs, the plate 199 is moved away from the cable driving gear 67 to decrease the compensating capacitance an equal amount and maintain the total capacitance of the antenna system unchanged. This results in presenting a constant capacitance to the radio receiver or other equipment to which the antenna is connected, regardless of variations in the length of the antenna.

FIGURE 6 shows a typical curve of capacity of the novel compensating arrangement of this invention versus the position of the antenna. This curve is, of course, determined by such variable factors as the pitch of the threads on the bushing sleeve 99 and the effective areas of the cable-driving gear 67 and the plate 109. Preferably the device is operated along a substantially linear portion of its operating curve, as shown, providing, for example, a variation between extremes of 56 mmf. and 48 mmf., as the length of the antenna device is changed between its fully extended and fully collapsed positions.

It will be apparent that the present invention provides a novel and practical mechanism for automatically compensating any variations in distributed capacitance in a whip-type antenna system whether motor-operated or manual types. The mechanism so provided is relatively inexpensive and rugged in construction and, yet, is reliable in operation.

While the illustrative embodiment of this invention has been described as a motor-controlled antenna system for a radio receiver mounted in an automobile, it will be appreciated that numerous applications of the principles of this invention will be obvious to one skilled in the art. Accordingly, the scope of this invention is not limited to the specific embodiment described but is only as defined by the appended claims.

I claim:

1. An antenna device having a substantially constant output capacitance over its entire length of structure comprising a number of telescoping sections to be ex tended in whip-like fashion or retracted, rack means of electrically conductive material having one end operative connected to one of said sections, means for driving said rack means to extend or retract said antenna device, said last-mentioned means including gear means electrically connected to and operatively engaging said rack means, terminal means connected to said sections for receiving signal energy from said antenna device, and compensating capacity means including a pair of movable plate members, one or" said plate members comprising said gear means, said compensating capacity means being continuously controllable in accordance with the extension and retraction of said antenna device to compensate for resulting variations in the distributed capacity across said antenna device thereby maintaining the output capacitance of said antenna device at said terminal means substantially constant.

2. An antenna device as set forth in claim 1 further including rotatable reel means connected to the other end of said rack means and wherein the other of said plate members is adapted on rotation of said reel means for displacement with respect to said one plate member whereby the magnitude of the compensating capacitance is varied.

3. An antenna device as set forth in claim 2 wherein gear means and said reel means are rotatably mounted on a shaft, said reel means being provided with a recess for receiving said other plate member, said other plate member being threadedly mounted along a portion of said shaft and engaging said reel means for rotation therewith and for translational movement relative thereto lengthwise of said shaft.

4. An antenna device comprising a plurality of sections to be telescopically extended and retracted to form an antenna of predetermined length, a flexible cable connected to the innermost one of said sections for extending and retracting said sections, gear means having its periphery shaped to operatively engage said cable, a guide member for receiving said cable and contoured to form a race for maintaining said cable in engagement with at least a portion of the periphery of said gear means, said race continuing thereafter at a gradually increasing radius and gradual deflection from the plane of said gear means whereby said cable is disengaged from said gear means, storage means arranged to receive said cable from said guide member, and compensating capacitive means comprising a first plate member and a second plate member, one of said plate members being electrically connected to said telescopic sections and the other of said plate members being electrically grounded, said second plate member being threadedly mounted on a shaft and engaged by said storage means for varying the distance between said first plate member and said second plate member upon the rotation of said storage means to compensate for variations in the distributed capacity of said antenna device in accordance with the variation in length of said antenna.

5. An antenna device as set forth in claim 4 wherein said first plate member comprises said gear means, said gear means being electrically integral with said telescopic sections along said cable, said gear means and said storage means being provided with central axial openings for mounting on said shaft, and further including means for electrically insulating said gear means and said second plate member.

References Cited in the file of this patent UNITED STATES PATENTS 1,561,228 Hammond Nov. 10, 1925 2,035,011 Rebotier Mar. 23, 1936 2,069,513 Wolfi Feb. 2, 1937 2,496,785 Finneburgh et al. Feb. 7, 1950 2,644,089 Bliss June 30, 1953 

1. AN ANTENNA DEVICE HAVING A SUBSTANTIALLY CONSTANT OUTPUT CAPACITANCE OVER ITS ENTIRE LENGTH OF STRUCTURE COMPRISING A NUMBER OF TELESCOPING SECTIONS TO BE EXTENDED IN WHIP-LIKE FASHION OR RETRACTED, RACK MEANS OF ELECTRICALLY CONDUCTIVE MATERIAL HAVING ONE END OPERATIVE CONNECTED TO ONE OF SAID SECTIONS, MEANS FOR DRIVING SAID RACK MEANS TO EXTEND OR RETRACT SAID ANTENNA DEVICE, SAID LAST-MENTIONED MEANS INCLUDING GEAR MEANS ELECTRICALLY CONNECTED TO AND OPERATIVELY ENGAGING SAID RACK MEANS, TERMINAL MEANS CONNECTED TO SAID SECTIONS FOR RECEIVING SIGNAL ENERGY FROM SAID ANTENNA DEVICE, AND COMPENSATING CAPACITY MEANS INCLUDING A PAIR OF MOVABLE PLATE MEMBERS, ONE OF SAID PLATE MEMBERS COMPRISING SAID GEAR MEANS, SAID COMPENSATING CAPACITY MEANS BEING CONTINUOUSLY CONTROLLABLE IN ACCORDANCE WITH THE EXTENSION AND RETRACTION OF SAID ANTENNA DEVICE TO COMPENSATE FOR RESULTING VARIATIONS IN THE DISTRIBUTED CAPACITY ACROSS SAID ANTENNA DEVICE THEREBY MAINTAINING THE OUTPUT CAPACITANCE OF SAID ANTENNA DEVICE AT SAID TERMINAL MEANS SUBSTANTIALLY CONSTANT. 